a) Field of the Invention
This invention generally relates to cameras and camera accessories, and more particularly, to systems for controlling the regions of focus within a field of view of a camera.
b) Description of the Prior Art
During the past century, since the invention of the still-type film camera, photographic technology has introduced many different types of cameras, usually identified by the format of film used. Today, for the most part, three main types of still-type film cameras are commercially available, 35 mm cameras (including point and shoot type camera, disposable cameras, single lens reflex cameras, and rangefinder type cameras), medium format cameras (including twin-lens), and large format cameras (including field-type and view type). These cameras use one of at least six basic systems of focusing: (1) fixed-focus, (2) “zone-focus”, (3) rangefinder-type focus, (4) twin-lens reflex ground glass, (5) single-lens reflex, and (6) automatic focus.
In a fixed-focus camera, such as a conventional disposable type camera, there is no means to control the focus of the lens. The focus of the lens is pre-set in the factory to provide acceptable focus at a predetermined distance (usually around 10 feet). This type of camera is essentially a pin-hole camera with a lens.
Camera operators using “zone-focus” cameras must estimate (or actually measure) the distance between the camera and the subject and use this information to control the focus of the lens so that the subject is reproduced in focus at the film plane of the camera.
A rangefinder focusing system uses an optical-mechanical device that produces two images in a viewfinder of the camera. The focusing device effectively functions as adistance measurer (or rangefinder) to help the operator determine the distance between the subject and the camera. In operation, as the operator adjusts the focus control of the lens, the two images within the viewfinder move with respect to each other. A subject is in focus when oth images overlap and appear as one image within the viewfinder.
A twin-reflex camera uses two identical lenses that include synchronized focus controls so that both lenses move simultaneously. One lens focuses an image onto a focusing screen for the operator while the other lens focuses essentially the same image onto the film plane. When the operator adjusts the first lens so that the image is in focus on the focusing screen, the second lens will be properly adjusted so that the image will also be in focus at the film plane.
The single-lens reflex focusing system (or SLR) is one of the most popular focusing systems used in today's cameras. This type of focusing system allows the operator to view the actual image that will be recorded by the film. A pivotal mirror rests in the path of incoming image light and is used to direct the image light from the lens to a focusing screen, which may be viewed by the operator through an eyepiece. The camera operator may manually (or with the assist of an automatic focusing system) adjust the lens focus until the desired image focus appears on the focusing screen. The focusing screen usually includes a focusing reticle to assist the operator in determining when the subject is in “true” image focus. When the shutter release button of the SLR camera is depressed, the pivotal mirror immediately pivots away from the path of incoming image light and allows the image light to continue to the film gate and film. The distance between the lens and the focusing screen is equal to the distance between the lens and the film plane so that a viewed focused image will be recorded in focus. This type of focusing system allows the camera operator to “sample” or test the focus adjustments of the particular lens before any film is exposed.
Finally, cameras that automatically focus include a battery-powered motor drive unit that directly controls the focus of the particular lens assembly, and at least one type of electronic distance sensor, such as sonar, infrared, or phase-contrast. The sonar and infrared sensors essentially determine the distance between the subject and the camera and then cause the motor to control the focus of the lens accordingly. The phase-contrast system measures the contrast of adjacent lines of the incoming image light and similarly, uses this information to control the focus of the lens.
Motion-film cameras or movie cameras typically use a zone-focusing system wherein the camera operator (or an assistant) will actively control the focus of a lens during a particular shoot. If the subject advances towards (or recedes away from) the camera, the camera operator may have to “rack focus” the lens during a shoot to maintain the moving subject within the depth of field of the lens in use and in focus on the film. Regardless of how the focus of a particular lens is adjusted, most of the motion-film cameras used today allow the cameraman to view the image through the lens (i.e., in an SLR manner).
Most of the above-described focusing systems are limited in that they are designed to focus an image evenly across the field of view as centered about a lens pupil (or a center axis). Furthermore, the focus of a lens is dependent on the depth of field of the particular lens. In turn, the depth of field is affected by the lens aperture, the focal length of the lens, and the distance between the camera and the subject. For example, a telephoto lens (having a large focal length, such as 400 mm) will yield a short or narrow depth of field (or depth of focus), resulting in only a slim portion of an object in the field of view being recording in sharp focus. In contrast, the depth of field of a wide angle lens (having a relatively short focal length, such as 14 mm or 28 mm) is close to infinite, resulting in all essentially objects in the field of view (foreground and background) being recorded in sharp focus. To this end, a director may create a mood or mystique within a particular shot by softening or de-focusing part of an image. For example, foreground actors and objects within a particular scene may be effectively “pushed” out from the depth of field (focus range) and thereby de-focused (which will effectively minimize their significance to the viewers), while a particular subject located further from the camera may be kept within the depth of field and will be recorded in focus on the film. Of course, in this situation, the audience will “focus” their attention on what is in focus in the image, the main subject.
Although this method of using the depth of field (created by either the aperture setting and/or the focal length of the lenses is quite effective at directing the audience to what is significant in the image, the method does have several limitations that severely constrain the director's creativity.
In the above example, the director would have to use a lens having mid to long focal lengths (e.g., telephoto) to obtain the desired selective de-focusing effect. Unfortunately, lenses with long focal lengths require a minimum focusing distance, typically between 10 and 20 feet. To achieve the desired selective de-focusing effect, the director would have to position the camera at least 10 feet from the subject. This minimum focusing distance requirement may not easily be met depending on the particular scene being shot. For example, the scene may be located within an elevator or on a submarine, or any other close-quartered environment wherein the minimum focusing distance requirement cannot be achieved without building a “specialized movie set”, or using soft-focusing techniques.
A common effects technique used in both still and motion photography to selectively de-focus or soften selective regions of a particular scene includes the use of a translucent medium, such as tissue paper, petroleum jelly or a frosted glass plate. The technique includes applying the translucent medium directly to (or positioning it in front of) the camera lens. The translucent medium effectively diffuses a select portion or region of image light entering the camera so that the resulting recorded image is softened, and selected detail is diluted. Although this de-focusing technique is somewhat effective at creating soft, de-focused regions of an image frame, the technique requires substantial setup time prior to shooting, and substantial clean-up time after the shoot. Also, the technique is difficult to control accurately in selecting exact image regions to dc-focus, and is further difficult to reproduce when a re-shoot is necessary, or in such instances wherein the actors actually move within the scene (which is, of course, often the case).
Also, using this well-known technique, in each situation of a shoot, all subjects located within the depth of focus will be recorded in focus on the film. The director cannot create an image wherein only one of two different subjects and/or objects within the same plane with respect to the camera is in focus. It would be desirable to record an image of a person, for example, wherein only their face and a smoking gun located in their hand (both located in the same image plane) are in focus.
Another technique available to photographers to de-focus or otherwise soften selected regions of an image frame includes what is called a “shift and tilt” mechanism, which pivotally connects a lens to a camera body. The shift and tilt mechanism allows a lens to both pivot and laterally shift with respect to a central optical camera axis, thus enabling a controlled distortion of selected regions of an image frame (to “shift” the lens means to slide it parallel to the viewfinder image, while keeping the lens' optical axis at right angles to the film plane). By tilting the lens up or down (or left or right), photographers can change the angle between the optical axis and the film plane. This allows the photographer to modify the plane of focus in the resulting photographs and in doing so, achieve a variety of effects. One such effect is the ability for the photographer to focus just a specific part of the subject.
A shift and tilt mechanism is used in most large format cameras and is available (as an attachment) for use with motion picture cameras. The mechanism is difficult to use and is subject to unwanted distortion, unless any of a limited number of dedicated lenses are used, which severely limits the director's creativity and control. Also, the regional focus-control offered by the shift and tilt mechanism is limited to single peripheral regions of the image frame, not multiple internally located regions, such as a central region within the image scene.
U.S. Pat. No. 6,167,206 of Hylen (Applicant) issued Dec. 26, 2000 and entitled “Image Modifiers for Use with Photography”, discloses a focus control system for use in photography wherein a modifier located at an intermediate focal plane within the lens system receives image light from the lens, the light is then relayed to the film. According to the patent, which is hereby incorporated by reference in its entirety, as if it were reprinted within the present specification, the modifier may be selectively deformed in such a manner as to create different regions of focus within a particular image, as the image light is projected onto the modifier and thereafter, re-focused onto the film. Applicant has been issued three other relevant patents all commonly assigned and of Hylen. These patents are: U.S. Pat. Nos. 6,285,834 6,201,933 5,649,259. These patents are similarly incorporated by reference, in their entirety.
U.S. Pat. No. 3,305,294 of Alvarez, issued Feb. 21, 1967 discloses a lens system for aberration correction and control in an optical system. The patented system includes a pair of bicubic phase profile optics, each an inverse of the other. When in perfect registration, the pair of optics produce a null wavefront and do not effect image light passing therethrough. However, translation of one optic relative to the other along one axis results in cylindrical focus (or de-focus) along the particular axis of translation (cylindrical focus or de-focus produces such focus or de-focus occurs only in vertical or horizontal strips, not symmetrically about the optical axis). Translation along both axes produces variable spherical or astigmatic power which may be used for wavefront correction or for a controlled aberration source.
U.S. Pat. No. 3,583,790 of Baker, issued Jun. 8, 1971, entitled “Variable Power, Analytic, Function, Optical Component in the Form of a Pair of Laterally Adjustable Plates having Shaped Surfaces, and Optical Systems Including such Components” discloses an optical assembly that uses at least two refracting plates. The plates are arranged generally perpendicular to an optical axis and adjacent to each other in a fitted orientation. The plates have quintic or higher order surfaces that are relatively movable laterally in such a manner that provides a zoom function within a lens system. The plates help correct spherical aberration within the lens system.
The above-described U.S. Pat. Nos. 3,305,294 of Alvarez, and 3,583,790 of Baker are hereby incorporated by reference, in their entirety.
It is accordingly an object of the invention to provide a focusing system for use with a camera which overcomes the limitations of the prior art.
It is another object of the invention to provide a focusing system for use with a camera which allows select regions of an image frame to be purposely de-focused in a controlled and efficient manner.
It is another object of the invention to provide a special effects device for use in photography which overcomes the limitations of the prior art.